ANI Models

The ANI (Accurate NeurAl networK engINe for Molecular Energies) family is a set of neural network potentials developed by the Roitberg group. ANI models are among the fastest ML potentials available, making them ideal for high-throughput screening and rapid prototyping of neutral organic molecular systems.

Available Variants

Model	Keyword	Elements	Training Level	Best For
ANI-2x	`ani2x`	H, C, N, O, F, S, Cl	ωB97X / 6-31G(d)	General organic chemistry with halogens
ANI-1x	`ani1x`	H, C, N, O	ωB97X / 6-31G(d)	Fast calculations on HCNO-only systems
ANI-1ccx	`ani1ccx`	H, C, N, O	CCSD(T)/CBS (transfer-learned)	Publication-quality accuracy for small molecules
ANI-1xnr	`ani1xnr`	H, C, N, O	ωB97X / 6-31G(d) (non-reactive)	Equilibrium geometries without bond-breaking

DFT-D4 Dispersion Correction

ANI models are the only models in MAPLE that support the DFT-D4 dispersion correction. D4 adds London dispersion (van der Waals) interactions, which is critical for non-covalent binding, molecular stacking, and conformational energetics.

#model=ani2x
#d4
#opt(method=lbfgs)

Tip

Always enable #d4 when studying systems with significant non-covalent interactions (hydrogen bonds, pi-stacking, host-guest complexes). The computational overhead is minimal.

Calculator Capabilities

Hessian: analytic and numerical Hessians are available in gas phase. Implicit-solvent Hessians (analytic or numerical) are not supported.
HVP: ANI is the only shipped backend that implements get_hvp() for the HVP-enabled Dimer path. ANI HVP is gas-phase only.
Implicit solvent: MAPLE's experimental GB-polar/QEq correction is energy-only (#sp with experimental=true); solvent forces, HVP, and Hessians are not supported.
Model files: MAPLE can auto-download ANI checkpoints from the MAPLE model repository, or you can provide an explicit model_path.

Usage Examples

General organic optimization

#model=ani2x
#device=gpu0
#opt(method=lbfgs)

0 1
C    0.000000    0.000000    0.000000
O    1.200000    0.000000    0.000000
H   -0.540000    0.940000    0.000000
H   -0.540000   -0.940000    0.000000

High-accuracy with coupled-cluster potential

#model=ani1ccx
#device=gpu0
#opt(method=lbfgs, level=extratight)

0 1
O    0.000000    0.000000    0.117300
H    0.000000    0.756900   -0.469200
H    0.000000   -0.756900   -0.469200

With D4 dispersion for non-covalent interactions

#model=ani2x
#d4
#device=gpu0
#opt(method=lbfgs, level=tight)

XYZ /path/to/dimer_complex.xyz

Limitations

No charge/multiplicity support. ANI models assume neutral, singlet ground state; use AIMNet2 or UMA omol for charged/open-shell inputs.
Limited elements. ANI-2x covers 7 elements; ANI-1x/1ccx/1xnr cover only H, C, N, O.
No periodic systems. ANI models do not support periodic boundary conditions.
Implicit solvation is energy-only. MAPLE's experimental GB-polar/QEq correction can be requested for #sp with experimental=true; solvent forces, optimization, MD, TS, scan, and frequency workflows remain unsupported for that correction.